Interference patterns for spiral-wound elements

ABSTRACT

Embodiments of the present invention provide for the deposition of spacing elements on both opposing surfaces of either an entire folded membrane sheet or portions thereof in combination with features deposited on portions of the same sheet to create spacing geometries not otherwise achievable.

TECHNICAL FIELD

The subject invention relates to a permeable membrane system useful forthe separation of fluid components, including spiral-wound membranepermeable membrane elements.

BACKGROUND ART

Spiral-wound membrane filtration elements consist of a laminatedstructure comprised of a membrane sheet sealed to or around a porouspermeate spacer which creates a path for removal of the fluid passingthrough the membrane to a central tube, while this laminated structureis wrapped spirally around the central tube and spaced from itself witha porous feed spacer to allow axial flow of the fluid through theelement. While this feed spacer is necessary to maintain open anduniform axial flow between the laminated structure, it is also a sourceof flow restriction and pressure drop within the axial flow channel andalso presents areas of restriction of flow and contact to the membranethat contribute significantly to membrane fouling via biological growth,scale formation, and particle capture.

Improvements to the design of spiral wound elements have been disclosedby Barger et al and Bradford et al., which replace the feed spacer withislands or protrusions either deposited or embossed directly onto theoutside or active surface of the membrane. This configuration isadvantageous in that it maintains spacing for axial flow through theelement while minimizing obstruction within the flow channel. It alsoeliminates the porous feed spacer as a separate component, thussimplifying element manufacture. Patent publication numberU52016-0008763-A1 entitled Improved Spiral Wound Element Constructionteaches the application of printed patterns on the back side of theactive surface of the membrane sheet, or directly on the surface of thepermeate spacer.

The following references, each of which is incorporated herein byreference, can facilitate understanding of the invention: U.S. Pat. Nos.3,962,096; 4,476,022; 4,756,835; 4,834,881; 4,855,058; 4,902,417;4,861,487; 6,632,357; and US application 2016-0008763-A1.

SUMMARY OF INVENTION

Embodiments of the present invention provide a membrane for use in aspiral wound filtration element, comprising a first leaf and a secondleaf, where each leaf has an active surface with a plurality ofprotrusions disposed on the surface, the protrusions being shaped anddisposed on the surface such that when the active surface of the firstleaf is placed adjacent to the active surface of the second leaf theprotrusions are in contact with each other, with the protrusions on thefirst leaf separated from the active surface of the second leaf by theprotrusions on the second leaf; where the first leaf and the second leafare placed with the active surfaces facing each other and separated bythe protrusions. The two leafs can be separate sheets of a suitablematerial, or can be provided by folding a single sheet, with each sideof the fold providing one leaf. Note that a membrane for use in a spiralwound filtration element inherently has two edges, the feed edge andreject edge, corresponding to the edges of the membrane that willencounter feed fluid flow and eject waste fluid flow respectively. Sucha membrane also inherently has a width, corresponding to the dimensionof the material between the feed and reject edges.

In some embodiments, the protrusions comprise a plurality of line-shapedprotrusions, where the line-shaped protrusions are disposed parallel toeach other and separated from each other in all planar directions on thesurface of the corresponding leaf; and wherein the line-shapedprotrusions are disposed on the surface at an angle other than 90degrees from the feed edge of the corresponding leaf such that theline-shaped protrusions on the first leaf contact the line-shapedprotrusions on the second leaf at their intersections. The line-shapedprotrusions can extend across the entire width of the leaf, or canextend across less than the entire width. In some embodiments, the angleis between 40 and 85 degrees, or between 100 and 135 degrees. In someembodiments, the protrusions protrude from the surface of each leaf byat least 0.065 mm but not more than 0.4 mm. In some embodiments, theprotrusions comprise a plurality of curved features, configured suchthat the curved feature on the first leaf will intersect the curvedfeatures on the second leaf at an angle other than 0 degrees when themembrane is spirally wound. In some embodiments, the line-shapedprotrusions are at least 20 mm long in the axial dimension (thecomponent of the length measured parallel to the axis of the center tubewhen spirally wound) and the spacing between line segments is less thanthe length of the line segments.

In some embodiments, the protrusions are disposed in a first region ofthe first leaf, and in a first region of the second leaf, the embodimentfurther comprises a plurality of flow protrusions disposed (a) on theactive surface of the first leaf other than in the first region of thefirst leaf, (b) on the active surface of the second leaf other than inthe first region of the second leaf, or (c) both, wherein the flowprotrusions have a height about equal to the sum of the height of theprotrusions in the first region of the first leaf and the height of theprotrusions in the first region of the second leaf, and wherein flowprotrusions on one leaf do not contact those on the other leaf when theelement is spiral wound.

In some embodiments, the line-shaped protrusions are disposed in regionsproximal the feed and reject edges of the corresponding leaf, and theembodiment further comprises a plurality of flow protrusions disposed(a) on the active surface of the first leaf in regions other than thoseoccupied by the line-shaped protrusions, (b) on the active surface ofthe second leaf in regions other than those occupied by the line-shapedprotrusions, or (c) both, wherein the flow protrusions have a heightabout equal to the sum of the height of the line-shaped protrusions onthe first leaf and the height of the line-shaped protrusions on thesecond leaf; and wherein the flow protrusions on one leaf do not contactthose on the other leaf when the element is spiral wound.

The present invention also provides a method of making a membrane,comprising providing a first leaf and a second leaf, each having anactive surface; placing a plurality of protrusions on the active surfaceof each leaf, the protrusions being shaped and disposed on the surfacesuch that when the active surface of the first leaf is placed adjacentto the active surface of the second leaf the protrusions are in contactwith each other with the protrusions on the first leaf separated fromthe active surface of the second leaf by the protrusions on the secondleaf; placing the active surface of the first leaf adjacent to theactive surface of the second leaf, separated by the protrusions.Providing a first leaf and a second leaf can comprise providing twoseparate sheets, or can comprise providing a sheet separated into afirst leaf and a second leaf by a fold line.

The present invention also provides a filtration element as thosedescribed herein, spirally wound around a center tube. The presentinvention also provides a fluid treatment system, comprising a pluralityof filtration elements as those described herein. The present inventionalso provides a method of treating a fluid, comprising flowing the fluidthrough a filtration element as those described herein.

Some embodiments provide a membrane for use in a spiral wound filtrationelement, comprising a sheet having an active surface, the sheet foldedwith the active surface inside the folded sheet, wherein the activesurface has a plurality of protrusions disposed thereon, the protrusionsbeing shaped and disposed on the surface such that the protrusionscontact each other and hold apart the facing active surfaces in thefolded sheet. In some embodiments, the protrusions comprise a pluralityof line-shaped protrusions disposed on the active surface at an angleother than 90 degrees to the feed edge of the membrane. In someembodiments, the angle is between 40 and 85 degrees, or between 100 and135 degrees. In some embodiments, the protrusions protrude from thesurface of the sheet by at least 0.065 mm but not more than 0.4 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of opposing patterns of solid lines onopposing faces of a single folded membrane leaf.

FIG. 2 is an illustration of opposing patterns of segmented lines onopposing faces of a single folded membrane leaf.

FIG. 3 is an illustration of a membrane leaf with half-height edgepatterns deposited along the full length of the inlet and outlet edgesof the leaf and full height features deposited on one half of themembrane leaf.

FIG. 4 is a representation of membrane feed spacers that have curvedlead in features on the feed end of the membrane element and that aretrimmed after rolling the element.

FIG. 5 is a representation of membrane feed spacers that have curvedlead in features on the feed end of the membrane element and curvedanti-telescoping device features to help avoid end blocking of theelement from high solids fluids.

FIG. 6 is a view of a flat, un-rolled spiral wound element with turningvanes having curved surfaces.

DESCRIPTION OF EMBODIMENTS AND INDUSTRIAL APPLICABILITY

Embossing or depositing features onto the surface of the membrane sheet,or onto or into the permeate carrier sheet of a spiral-wound element toprovide spacing between adjacent membrane sheets can provide severaladvantages as compared to feed spacer mesh including more open flowchannels, lower pressure drop, reduced fouling, and the ability toproduce thinner feed space than is practical using a mesh. Variousconfigurations have been disclosed by Barger et al, Bradford et al, andin PCT/US2014/018813. Embodiments of the present invention provide theuse of printed or otherwise deposited surface features that selectivelycontact one another to provide spacing between adjacent membrane sheetsto create unique contact and flow patterns not achievable by depositionof isolated islands. The patterns created thereby may also contain otherdeposited features that do not contact one another to provide additionalspacing and flow direction within the spiral-wound element.Additionally, variable heights of printed or otherwise depositedfeatures can be employed to produce different spacer geometries ondifferent areas of the spiral-wound element.

Previous disclosures of printing, embossing, or otherwise depositingfeatures to provide feed spacing in spiral-wound elements typicallyinvolve deposition of the features on one half of each folded membraneleaf to provide the spacing while eliminating the possibility of havingthe features contact one another or stack when the leaf is folded.Contact and geometry considerations are made more complex when aspiral-wound element is rolled because of the changing radii of the leafsections to one another and to the rest of the components of theelement. In some cases, however, having spacing elements depositedacross all or part of the membrane surface which are designed to contactone another upon folding can be beneficial. Deposition patterns orfeatures can be configured such that when the sheet is folded androlled, there is no possibility at any point for the patterns to nestwithin the opposing pattern and feature-to-feature contact is ensuredrather than feature-to-membrane contact.

In an example embodiment shown in FIG. 1, a series of continuous angledparallel lines 10 are deposited on the membrane surface extending fromthe edge corresponding to the inlet flow of the rolled element to theedge corresponding to the outlet flow. In this example, the printedlines can be between 0.065 mm and 0.80 mm wide and from 0.065 mm to 0.40mm tall. Spacing between adjacent elements should be close enough toprevent collapse of the membrane sheet between the parallel lines duringmembrane rolling due to the viscosity of the adhesive used to form theenvelope between the membrane sheet, the adjacent permeate carrier andthe next membrane sheet. For materials in common use today, this spacingcan be no more than 3 mm from one line to the next, and more preferablyis 2.5 mm. Any angle between 0° and 90° or between 90° and 180° from theinlet flow edge 14 can be used to ensure feature to feature contact onthe folded leaf, but angles in the ranges from 45-80° or 100-135° can bemore suitable to maintain acceptable flow and pressure drop through theelement. When folded, the deposited patterns 10 will contact theopposite pattern 12 at a supplementary angle such that the depositedpatterns will repeatedly cross and support each other without lettingthe pattern from the opposite side contact the membrane film directly.The lines can be straight lines as shown, and can also be curved,sinusoidal, or otherwise shaped provided they contain no extendedsegments (e.g. <10 mm) where the pattern is near 90°. Patterns that arenot straight lines can be chosen for particular performancecharacteristics, e.g., to improve mixing or to lengthen or shorten theflow path across the membrane surface.

In another example embodiment shown in FIG. 2, line segments 20 can beused instead of continuous lines to produce the pattern that willcontact itself 22 when folded. In this example, the printed pattern canbe between 0.065 mm and 0.80 mm wide and from 0.065 mm to 0.40 mm tall.Spacing between adjacent elements should be close enough to preventcollapse of the membrane sheet between the parallel lines duringmembrane rolling due to the viscosity of the adhesive used to form theenvelope between the membrane sheet, the adjacent permeate carrier andthe next membrane sheet. With materials in common use today, thisspacing can be no more than 3 mm from one line to the next, and morepreferably is 2.mm. Any angle between 0° and 90° or between 90° and 180°from the inlet flow edge 24 can be used to ensure feature to featurecontact on the folded leaf, but angles in the ranges from 45-80° or100-135° can be more suitable to maintain acceptable flow and pressuredrop through the element. Rolling of a spiral-wound element, even whendone in an automated fashion, is still inexact. Typically folded leaveswithin a given element are able to move as much as +/−10 mm axially tothe center tube of the element due to movement of the various sheetmaterials and glue used in assembly. As such, minimum feature length ofbeyond 20 mm in the axial dimension will generally be needed to ensurecontact between adjacent features in folded leaves. Gaps betweenadjacent line segments in the axial dimension are shorter than thefeature length in the axial dimension to avoid any possibility ofnesting of features when folded. In this embodiment the line segmentscan also be straight, curved, sinusoidal, or otherwise repetitivelyvarying.

Maintaining open spacing at the inlet and outlet edges of the elementwhile minimizing flow restriction within the flow channel can also beenhanced by combining full leaf length deposition where features meet tosupport each other when folded with areas of feature deposition that arenot designed to interfere with adjacent features after folding. Thisallows the patterns that are not designed to interfere with adjacentfeatures after folding to comprise a variety of shapes that are notlimited to lines or line segments, such as circular or polygonal posts,curved line segments or other shapes that alter flow in a desirablemanner. In an example shown in FIG. 3, the printed interference pattern30 along the inlet 32 and outlet 34 edges can be between 0.065 mm and0.80 mm wide and from 0.065 mm to 0.40 mm tall, and extend from 40 mm to80 mm axially from the inlet and outlet edge of the membrane leaf. Anyangle between 0° and 90° or between 90° and 180° from the inlet andoutlet flow edge can be used to ensure feature to feature contact on thefolded leaf, but angles in the ranges from 45-80° or 100-135° can bemore suitable to maintain acceptable flow and pressure drop through theelement. Another pattern is deposited in the center section 30 on halfof the membrane leaf and can be twice as tall as the features on theedges so that, when the leaf is folded along its center line 38, thespacing on the edges and the central area is uniform. In general thepatterns deposited at the edge are spaced more densely to support theglue line used to bond the leaves together while the central pattern arespaced more sparsely to allow less restricted flow through this portionof the element.

In a specific example embodiment a pattern of solid line segments 30,0.6 mm wide and 93 mm long, is deposited extending from the inlet 32 andoutlet 34 edge, at an angle of 45° relative to the edge of the membranesheet such that it extends 66 mm inward onto the leaf at a height thatis one half the desired finished feed space height, in this case 0.2 mmfor a 0.4 mm total feed spacing after folding. Another pattern, a squarearray of circular posts 36, 1.2 mm in diameter spaced 6.5 mm from oneanother, is then deposited on the central area between the two 0.2 mmpatterns to a height of 0.4 mm. This pattern is only deposited alongone-half the length of the overall leaf such that when the leaf isfolded in half at the center line 38, the edge patterns contact oneanother to create 0.4 mm feed space at the edges while the centralpattern creates the 0.4 mm spacing in the middle of the leaf.

In another embodiment of the present invention shown in FIG. 4, curvedinlet brine feed spacer features can be utilized. These features can beprinted or deposited on one half of the membrane leaf along the inletand outlet edges and only extend far enough to provide support to thearea of the glue line. During rolling and gluing the element, the curvedfeatures 44 at the inlet and outlet edge create a tighter pattern wherethe tips 46 approach one another such that during rolling the patternsprovide support to the adjacent layer as the spiral wound element isrolled. In another embodiment of the present invention shown in FIG. 5,the space between tips 46 can be reduced to zero thereby making acontinuous solid line 48 that provides more complete support of the glueline during rolling operations. After the ends of the element aretrimmed at trim line 40, the tighter spacing of the curved portions isremoved which opens up the inlet and outlet spacing between the featuresto facilitate fluid flow and help avoid pressure losses at the ends ofthe element. In conventional spiral wound membranes, the flow of fluidinto the brine feed spaces is normal (flow vector is parallel to theaxis of the center tube) to the end of the element, and materials in thefluid stream can stack up at the end of the brine feed channels andthereby block the fluid feed channels. This fluid blockage at the feedend of the element can be mitigated by creating a fluid flow stream thatis partially diverted in a flow vector that is at an angle from thecenterline of the element. By creating a sweeping motion of fluid as itenters the brine feed spaces, materials that might have accumulated atthe feed spaces can be swept away. In FIG. 6, turning vanes 60 havecurved surfaces that impart a lateral flow at the end of the rolledelement to help avoid end blocking of the element by sweeping solids inthe fluid stream from the end face of the spiral wound element that canbe entering the brine feed space channels of the spiral wound element.The view of FIG. 6 is shown as a flat, un-rolled view of a spiral woundelement. Normally, this pattern is wrapped around a center tube, but isshown in FIG. 6 to more easily describe the concept. Brine feed solution66 is normal (parallel to the axis of the center tube) as it enters theend of the spiral wound element. Turning vanes 60 impart a flow patternthat is across the end of the spiral wound element thereby keepingmaterial from accumulating on the end of the brine feed channel. As theprinted spacers 64 enter the element, there is a curved inlet component62 that maintains the brine feed solution 66 in line with the flowvector of brine feed solution 66. As brine feed solution enters themembrane feed space, printed spacers 64 help align the flow vector ofbrine feed solution 66 to be more parallel to the center line of themembrane element center tube. However, it will be known to thosefamiliar with the prior art that these printed spacers 64 can havevarious shapes and configurations to stimulate localized vorticity andreduce concentration polarization in the brine feed spaces of the spiralwound element.

The features can be deposited by a variety of techniques. Traditionalprinting techniques such as offset printing, gravure printing, andscreen printing, can be suitable, although there might be thickness andgeometry limitations with these deposition techniques. Thicker featurescan be deposited by microdispensing, inkjet printing, fused deposition,photo polymer technology, hot melt polymers, or via application using anadhesive that can include roll transfer of sheet or pick-and-place ofindividual features.

The features can be comprised of any number of materials which arecompatible with the separated fluid and the permeate carrier including,but not limited to, thermoplastics, reactive polymers, waxes, or resins.Additionally, materials that are compatible with the separated fluid butnot compatible with direct deposition to the membrane sheet, including,but not limited to high-temperature thermoplastics, metals, or ceramics,can be pre-formed, cast, or cut to the proper dimensions and adhered tothe surface of the membrane sheet with an adhesive that is compatiblewith the membrane sheet.

The present invention has been described in connection with variousexample embodiments. It will be understood that the above description ismerely illustrative of the applications of the principles of the presentinvention, the scope of which is to be determined by the claims viewedin light of the specification. Other variants and modifications of theinvention will be apparent to those skilled in the art.

We claim:
 1. A membrane for use in a spiral wound filtration element,comprising a first leaf and a second leaf, where each leaf has an activesurface with a plurality of protrusions disposed on the active surface,the first leaf and second leaf disposed with the active surfaces facingeach other, the protrusions shaped and disposed on the active surfacessuch that the protrusions on the first leaf are in contact with theprotrusions on the second leaf, with the protrusions on the first leafseparated from the active surface of the second leaf by the protrusionson the second leaf.
 2. A membrane as in claim 3, comprising a sheet ofmembrane material folded along a fold line, wherein the first leafcomprises a first portion of the sheet; and the second leaf comprises asecond portion of the sheet, separated from the first portion by a foldline.
 3. A membrane as in claim 1, wherein the protrusions comprise aplurality of line-shaped protrusions, where the line-shaped protrusionsare disposed parallel to each other and separated from each other in allplanar directions on the surface of the corresponding leaf; and whereinthe line-shaped protrusions are disposed on the surface at an angleother than 90 degrees from the feed edge of the corresponding leaf suchthat the line-shaped protrusions on the first leaf contact theline-shaped protrusions on the second leaf at their intersections.
 4. Amembrane as in claim 3, wherein the angle is between 40 and 85 degrees,or between 100 and 135 degrees.
 5. A membrane as in claim 3, wherein theprotrusions protrude from the surface of each leaf by at least 0.065 mmbut not more than 0.4 mm.
 6. A membrane as in claim 1, wherein theprotrusions comprise a plurality of curved features, configured suchthat the curved feature on the first leaf will intersect the curvedfeatures on the second leaf at an angle other than 0 degrees when themembrane is spirally wound.
 7. A membrane as in claim 3, wherein theline-shaped protrusions extend across the entire width of thecorresponding leaf.
 8. A membrane as in claim 3, wherein the line-shapedprotrusions extend across less than the entire width of thecorresponding leaf.
 9. A membrane as in claim 8 wherein the line-shapedprotrusions are at least 20 mm long in the axial dimension and thespacing between line segments is less than the length of the linesegments.
 10. A membrane as in claim 1, wherein the protrusions aredisposed in a first region of the first leaf, and in a first region ofthe second leaf, and further comprising a plurality of flow protrusionsdisposed (a) on the active surface of the first leaf other than in thefirst region of the first leaf, (b) on the active surface of the secondleaf other than in the first region of the second leaf, or (c) both,wherein the flow protrusions have a height about equal to the sum of theheight of the protrusions in the first region of the first leaf and theheight of the protrusions in the first region of the second leaf, andwherein flow protrusions on one leaf are not in contact with those onthe other leaf.
 11. A membrane as in claim 10, wherein the flowprotrusions are disposed on the first leaf and not on the second leaf.12. A membrane as in claim 8, wherein the line-shaped protrusions aredisposed in regions proximal the feed and reject edges of thecorresponding leaf, and further comprising a plurality of flowprotrusions disposed (a) on the active surface of the first leaf inregions other than those occupied by the line-shaped protrusions, (b) onthe active surface of the second leaf in regions other than thoseoccupied by the line-shaped protrusions, or (c) both, wherein the flowprotrusions have a height about equal to the sum of the height of theline-shaped protrusions on the first leaf and the height of theline-shaped protrusions on the second leaf; and wherein the flowprotrusions on one leaf do not contact those on the other leaf when theelement is spiral wound.
 13. A membrane as in claim 12, wherein the flowprotrusions are disposed on the first leaf and not on the second leaf.14. A method of making a membrane as in claim 3, comprising providing afirst leaf and a second leaf, each having an active surface; placing aplurality of protrusions on the active surface of each leaf; placing theactive surface of the first leaf adjacent to the active surface of thesecond leaf, separated by the protrusions; wherein the protrusions areshaped and disposed on the active surfaces such that the protrusions onthe first leaf are in contact with the protrusions on the second leaf,with the protrusions on the first leaf separated from the active surfaceof the second leaf by the protrusions on the second leaf.
 15. A methodas in claim 14, wherein providing a first leaf and a second leafcomprises providing a sheet separated into a first leaf and a secondleaf by a fold line; and wherein placing the active surface of the firstleaf adjacent to the active surface of the second leaf comprises foldingthe sheet along the fold line.
 16. A filtration element comprising amembrane as in claim 3, spirally wound around a center tube.